254 Th. Mortensen. 



lient part of an adambulacral plate with the attached long median 

 spine and the shorter lateral spines (those of the one side). 



From this explanation of the "vexillum" it further follows that 

 the shallow groove found by Bell at its upper end is only the 

 surface of fracture. That the grooves in the "vexillum" described 

 and figured by Danielssen and Ko ren are only the result of bad 

 preparation has already been shown by Grieg. I have, upon the 

 whole, been unable to find any groove in this spine on either side 

 of it, and I have carefully examined from all sides several of these 

 spines, cleaned with Eau de Javelle. They are, indeed, simply 

 flattened. The "etwas rauhen Ränder" (Grieg) of the supposed 

 furrow are nothing peculiar for these spines; the edge of the spine 

 is only somewhat irregular as is generally the case in such irregular 

 calcareous network, not developed into any special structure. 



Bell (Op. cit. p. 229) describes the orifices for the passage of 

 the tubefeet as "very deeply set, and the walls are so excavated as 

 to form a pit which shelves inwards (PI. XXIV, Fig. 2)". This is 

 only the result of the drying of the animal. The openings are very 

 large, but otherwise quite as usual in Asteroids and wholly occupied 

 by the somewhat extraordinarily large and powerful tubefeet, which, 

 evidently, must enable the animal to walk with considerable 

 swiftness. The very large and muscular ampullæ (PI. XIV. Fig. 2) 

 also afford evidence that the tubefeet of this species must be 

 unusually active locomotor organs. In sections it is seen that the 

 musculature is exceedingly developed, projecting into the lumen of 

 the ampulla (PI. XVII. Fig. 8). 



A curious feature is observed on the tubefeet, viz. that they are 

 in their basal part set with irregular papillæ, which may even be 

 distinctly stalked; they may be up to 2 mm long (PI. XVII. Fig. 14). 

 That these papillæ cannot be simply the result of the contraction of 

 the tubefeet seems evident (the fine lamellar structure of the skin 

 of the tubefeet, on the other hand, is certainly only caused by the 

 contraction). It seems not unreasonable to suggest that they may 

 have some sensory function. 



4. Pontaster tenuispinus (Dub. & Kor.). 



Astropectentenuispimis Dub en och Koren. 1844. Öfversigt af Skan- 

 dinaviens Echinodermer. Vet. Akad. Handl. 

 Stockholm, p. 251. PI. VIII. Figs. 20— 22. 



Archaster — M. Sars. 1861. Norges Echinodermer. p. 38. 



PI. III. Figs. 5—7. 

 — — Danielssen & Koren. 1884. Norske Nord- 



havs Exp. Asteroidea. p. 85. 



